For transferring heat energy from one process medium to a second process medium, use is made of heat exchangers. In recuperative heat exchangers, each medium has a space that is separated from the other medium.
A widespread design of heat exchangers consists of so-called tube-bundle heat exchangers wherein a medium is conducted through a plurality of parallel tubes arranged in a bundle. The second medium is conducted through a chamber surrounding the tube bundle.
According to a special design, the tube bundle is formed by a plurality of tubes that are closed on one side. These tubes have a second tube inserted into them that is open toward the closed end of the first tube. A design of this type is known from US 2010/0254891 A1. Since, for improved convenience of connection, the inner tubes are often guided laterally out from the inner tube, this design is often referred to as a bayonet-type heat exchanger.
This design offers the advantage that the medium, mostly flowing back in the inner tube, will transmit a part of the thermal energy to the medium flowing by on the outside and thus will contribute to the heating of the inflowing cooler medium.
In heat exchangers of this type, however, problems are encountered in the realization of an advantageous control, and further problems may occur when the system must be switched off urgently, e.g. when the to-be-heated medium is exposed to an excessive temperature.
Thus, it is an object of the invention to provide a heat exchanger of the initially mentioned type wherein a switch-off of the heat transmission is possible in an advantageous manner. Further, preferably, an advantageous control of the heat exchanger should be possible.